1. Field of the Invention
The present invention relates to geared motors. More particularly, it relates to a series of geared motors which are well suited for preparing various geared motors as a plurality of groups of products on the basis of technically reasonable ideas.
2. Description of the Prior Art
Heretofore, some series of geared motors, which include various motors combined with speed change gears and in each of which a plurality of change gear ratios can be selected, have been put on the market.
In the series of geared motors of this type, several kinds of sizes (assorted dimensions) generally called "frame work Nos." are set in conformity with mating machines. A plurality of change gear ratios are prepared for each "frame work No.". Each user may choose a geared motor which has a torque (capacity), a size or a rotational speed meeting a particular purpose, from within the series of geared motors classified as stated above.
As the geared motors in such series, there have hitherto been known ones in which a so-called "simple planetary gear mechanism" is adopted as the speed change mechanism of the speed change gears. The simple planetary gear mechanism includes a sun gear, a planet gear which meshes with the sun gear by means of outer gearing, and an internal gear with which the planet gear meshes by inner gearing.
Incidentally, the speed change gears function as "reduction gears" when used for lowering the rotational speed of a motor, and as "speedup gears" when used for raising the rotational speed of the motor by reversing the input and output of the identical speed change gears. The use as the reduction gears shall be mentioned below for the sake of convenience, and will be concretely explained with reference to FIG. 14.
First and second reduction portions A and B are respectively assembled in the reduction gears, and the simple planetary gear mechanism is adopted for both of them.
Both the first and second reduction portions A and B are similarly constructed. The first reduction portion A (the second reduction portion B) includes a sun gear 602 (702) which is endowed with a floating construction in order to realize an equal load distribution, a planet gear 604 (704) which meshes with the sun gear 602 (702) by outer gearing, and an internal gear 606 (706) with which the planet gear 604 (704) meshes by inner gearing. The planet gear 604 (704) is held by a planet frame or disc 608 (a planet frame or output shaft flange 708) which is arranged on one axial side thereof.
The operation of the reduction gears will be briefly explained together with the other constructions thereof.
When an input shaft 610 is rotated, the sun gear 602 of the first reduction portion A is rotated through a coupling 611. In accordance with the rotation of the sun gear 602, the planet gear 604 revolves round the sun gear 602 by inner gearing with the internal gear 606 which is fixed to a casing 612.
The planet gear 604 is supported through a bearing 616 by a supporting pin 614, the revolution around the sun gear 602 is transmitted to the disc (planet frame) 608. When the disc 608 is rotated, the sun gear 702 of the second reduction portion B connected to the disc 608 is rotated. In accordance with the rotation of the sun gear 702, the planet gear 704 revolves round the sun gear 702 by inner gearing with the internal gear 706 which is fixed to the casing 612.
The planet gear 704 is supported through a bearing 716 by a supporting pin 714, the revolution around the sun gear 702 is transmitted to the output shaft flange (planet frame) 708. The output shaft flange 708 is in spline connection with an output shaft 620, so that the output shaft 620 is rotated by the rotation of the output shaft flange 708.
In the geared motor which adopts such a simple planetary gear mechanism as the speed reduction mechanism of the reduction gears, the speed reduction mechanism can be constructed in a single stage ordinarily for reduction gear ratios of 1/3-1/9 or so. With the simple planetary gear mechanism, however, it is structurally difficult to attain a reduction gear ratio lower than 1/3, and it is especially impossible in theory to attain a reduction gear ratio of 1/2. It is accordingly common practice to set only the ratios of 1/3 and higher as the reduction gear ratios which are made ready within the identical framework No. in the specific series.
On the other hand, the simple planetary gear mechanism of the single-stage type is difficult of attaining a reduction gear ratio higher than 1/9, for example, a "high" reduction gear ratio of 1/30 or 1/100. (In this specification, a "high" ratio shall mean a large magnitude of gear change. Accordingly, the "high" reduction gear ratio has a comparatively small value, whereas a "high" speedup ratio has a comparatively large value. A "low" ratio will be self-explanatory.) In general, therefore, such a "high" reduction gear ratio is attained by the two-stage type as in the prior-art example stated above, or by a three-stage type. The multistage type, however, is problematic as explained below. When it is intended to simultaneously realize the "low" reduction gear ratios and the "high" reduction gear ratios (that is, to prepare a product having both the "low" and "high" ratios) in the identical framework No., in other words, under the condition that the assorted dimensions (sizes) for the mating machines are the same, the reduction gears on the side of the "low" reduction gear ratios become unnecessarily large in size. This incurs a waste as the whole series. It is accordingly the actual situation that the reduction gears of very "high" ratios are not normally made in a series of geared motors adopting the simple planetary gear mechanism.
Meanwhile, as series of geared motors affording reduction gears of comparatively "high" ratios, there have hitherto been marketed ones in which a planetary gear mechanism having an oscillating inner gearing system is adopted as the mechanism of the reduction gears of the geared motors.
The planetary gear mechanism of the oscillating inner gearing system includes a first shaft, an eccentric body which is attached on the first shaft, an external gear which is mounted so as to be capable of eccentrically rotating relative to the first shaft through the eccentric body, an internal gear with which the external gear meshes by inner gearing, and a second shaft which is connected to the external gear through means for transmitting only the component of the revolution of the external gear on the axis thereof. This planetary gear mechanism is known as one in which reduction gear ratios of 1/6-1/119 or so can be realized in one stage.
A practicable structural example is illustrated in FIGS. 15 and 16. This example has offered the above planetary gear mechanism to the "geared motor for speed reduction" in such a way that the first shaft is set as an input shaft (connected with a motor), while the second shaft is set as an output shaft, and that the internal gear is fixed.
Referring to FIGS. 15 and 16, an eccentric body 870 is snugly fitted on an input shaft 810 through a key 872. An external gear 876 is mounted on the eccentric body 870 through a bearing 874. The external gear 876 is provided with a plurality of inner roller holes 878, in each of which an inner pin 814 and an inner roller 814A are inserted.
The external gear 876 is formed at its outer periphery with outward teeth 877 each of which has a trochoidal tooth profile, a circular arc tooth profile or the like. The outward teeth 877 are in inner gearing with an internal gear 806 which is fixed to a casing 812. The inward teeth of the internal gear 806 are concretely so constructed that outer pins 880 are held easy of rotation by the sliding engagement thereof with the walls of corresponding outer pin holes 882.
The inner pins 814 each penetrating through the external gear 876 are fixed to the flange part 808 of an output shaft 820. The flange part 808 is connected with the input shaft 810 through an output side bearing 874.
When the input shaft 810 is rotated one revolution, the eccentric body 870 performs one revolution. In accordance with the revolution of the eccentric body 870, the external gear 876 is about to oscillatingly rotate round the input shaft 810. Since, however, the external gear 876 has its revolution on the axis thereof restricted by the internal gear 806, it almost performs only oscillations in inner gearing with the internal gear 806.
Assuming by way of example here that the number of teeth of the external gear 876 is N and that the number of teeth of the internal gear 806 is N+1, the difference between the numbers of teeth is 1 (one). Therefore, each time the input shaft 810 performs one revolution, the external gear 876 rotates only in correspondence with one tooth relative to the internal gear 806 fixed to the casing 812 (that is, it revolves on its axis to the amount of one tooth). This signifies that one revolution of the input shaft 810 is reduced to -1/N revolution of the external gear 876. Incidentally, the minus sign signifies the reverse rotation.
Herein, while the oscillating component of the revolution of the external gear 876 is absorbed by clearances defined between the inner roller holes 878 and the corresponding inner rollers 814A, only the component thereof on the axis of the external gear 876 is transmitted to the output shaft 820 through the inner pins 814.
Thus, the speed reduction at the reduction gear ratio of -1/N is eventually achieved.
In the prior-art example, the internal gear of the inner-gearing planetary gear mechanism is fixed, and the first shaft and second shaft are respectively employed as the input shaft (connected with the motor) and output shaft. Alternatively, however, reduction gears for a geared motor can also be constructed by fixing the second shaft and employing the first shaft and internal gear as the input shaft and output shaft, respectively. Further, speedup gears for a geared motor for speedup use can be constructed by reversing the input and output of the above speed change gears.
As already stated, the series of geared motors adopting the simple planetary gear mechanism in the prior art are structurally difficult of attaining the change gear ratio lower than 1/3, and they are theoretically incapable of attaining the change gear ratio of 1/2. Therefore, a geared motor affording the change gear ratio of 1/2 has never been prepared within the identical framework No. in the specific series.
On the other hand, regarding "medium" and "high" change gear ratios (the "medium" ratio being intermediated between the "low" and "high" ratios), geared motors in which change gear ratios of, for example, 1/3-1/100 are made ready in an identical series have not hitherto been offered, either. It has accordingly been impossible for each user to freely replace his/her geared motor with a geared motor of the same assorted dimensions differing in only the change gear ratio.
This point will be explained in more detail.
As stated before, in the series of geared motors adopting the planetary gear mechanism of the oscillating inner gearing system in the prior art, only the change gear ratios of 1/6 and higher have been made ready. This is ascribable to the fact that the oscillating inner-gearing planetary gear mechanism is difficult of setting a change gear ratio lower than 1/6 in relation to the speed reduction mechanism thereof. Accordingly, the user who wants to attain the change gear ratio lower than 1/6 has hitherto inevitably selected a geared motor which belongs to another series, for example, the series of geared motors employing the preceding simple planetary gear mechanism.
Why the two different series have heretofore been separately existent, is chiefly based on technical reasons as explained below.
Originally, a low output shaft speed and a "high" change gear ratio (a high torque) are often intended in the geared motor adopting the planetary gear mechanism of the oscillating inner gearing system. Inevitably, the sizes of an output shaft etc. for mating machines become large relative to the size of a motor. Moreover, noise reduction is required of the geared motor in many cases.
In contrast, a comparatively high output shaft speed and a "low" reduction gear ratio (a low torque) are needed in the geared motor adopting the simple planetary gear mechanism. Accordingly, the sizes of an output shaft etc. for mating machines may be small relative to the size of a motor. Therefore, it results in a weight increase and an excessive quality and it is difficult to conform the sizes of the output shafts to those of the series of the planetary gear mechanism of the oscillating inner gearing system.
Besides, in the geared motors of the simple planetary gear mechanism, the construction of floating a sun gear is generally adopted in order to realize an "equal load distribution" in compliance with the request of keeping favorable high-speed rotations for a long term. This leads to the problem that noise reduction in the simple planetary gear mechanism is difficult. The problem is inconsistent with the series of the planetary gear mechanism making use of the oscillating inner gearing system which is eagerly requested to reduce the noise.
The situation where the geared motors can be supplied in only the different series with the boundary at the change gear ratio around 1/6 in this manner, incurs various drawbacks in the aspect of convenience in use or in the aspect of pure technology.
By way of example, let's consider a case where the user having a certain material handling equipment being driven at the change gear ratio of 1/6 wants to lower the ratio to about 1/5 by any cause. In this case, the series of the geared motors which can be supplied differs from that of the user's geared motor, so that both the series are different in all of the assorted dimensions with the material handling equipment, the diameter of the output shaft, the height of the axis of the geared motor (as measured from the mounting plane of the geared motor), etc. Moreover, even the sorts of the motors (concretely, the torque or the basic rotational speed of the motor) are sometimes different. Therefore, the design of the installed machine needs to be altered considerably on the user side.
Also in the aspect of technical performance, in a case where the geared motor at the change gear ratio of 1/6 has been replaced with the geared motor at the ratio of 1/5 by way of example, the user must submit to problems such as an abrupt increase in noise, because of the different design concepts of both the geared motors. That is, the user cannot introduce the new geared motor of the slightly different change gear ratio while keeping the continuity of the performance, in spite of the geared motors of identical in-line type. Besides, the geared motors in the different series are not interchangeable or exchangeable at all in points of the size and the capacity.
Further, from the viewpoints of the interchangeability or exchangeability, in any of the series of geared motors in the prior art, the exchange of a motor requires the overhaul of most part of speed change gears for changing oil seals etc. and the subsequent reassemblage thereof. As a result, a serious problem to be stated below has been posed.
In recent years, various capabilities have been required of motors to be adopted in accordance with intended uses, in fields utilizing such geared motors (for example, in the field of material handling systems). By way of example, in spite of the same horsepower, there have come into uses multifarious motors with accessory control circuits taken into account, such as a mere induction motor which is conventional, a motor which is furnished with a brake, a motor which undergoes only a slight backlash and therefore incurs no positional shift even in a reciprocating motion, a motor which has an inverter control circuit and can accordingly control revolutions per minute at a constant torque, and a motor which is completely rendered waterproof in order to enhance safety.
Much importance is accordingly attached, not only to the requirement that the geared motor itself can be assembled in a short time period at the assembling stage thereof, but also to the requirement that the motor which is currently installed and used in, for example, the material handling system can be exchanged with ease and in a short time period in compliance with an altered purpose. Herein, it cannot satisfy the requirement of nowadays that the speed change gears must be mostly overhauled in the exchange of the motor as stated above.
In addition to such circumstances, the selection of the geared motor in the different series has heretofore been necessitated due to the slightly different change gear ratio as explained above. In the case of involving the alteration of the change gear ratio of or near 1/6, therefore, it has been quite impossible to meet the requirement that only the motor is exchanged in the short time period in compliance with the user's purpose.